What happened
On 9 April 2008, a Jetstream 41, registration G-MAJV, departed Aberdeen for the Faroe Islands in snowy and freezing conditions. Although the aircraft had been swept for snow by ground staff, it had not undergone formal de-icing or anti-icing procedures. The commander, believing the wings were clear and the tail section had been adequately addressed, proceeded with the departure to avoid further delays.
During the climb through FL90, the autopilot pitch trim warning activated. Upon disengately the autopilot, the crew discovered that the elevators had become immovable. The pilots attempted to regain control by applying significant physical force to the control columns and varying engine power. Through these efforts, the crew managed to induce oscillations that eventually allowed the aircraft to descend into warmer air, where the ice began to melt. At approximately 4,000 feet, the controls became free again, and the aircraft was safely landed at Wick.
The investigation
The AAIB investigation focused on the state of the aircraft's surfaces and the procedures followed prior to takeoff. Investigators examined the aircraft's flight data recorder and cockpit voice recorder, which revealed that the elevator trim system appeared to be operating in reverse, causing the aircraft to pitch up when a pitch-down command was applied.
Physical examination of the aircraft's tailplane following the incident revealed ice present within the elevator hinges. While the de-icing and anti-icing systems were found to be fully functional, the investigation looked into why the aircraft was operated without adequate protection against further ice accretion during the flight.